9643 ‎(2)‎

• UCREFRP Catalog Number: 9643
• Author: Seener, J. W.
• Title: Inbreeding Depression and the Survival of Zoo Populations
• USFW Year: n.d.
• USFW - Doc Type: 209-217
• Copyright Material: YES

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INTRODUCED FISHES OF THE LOWER COLORADO 85
Smallmouth bass stomachs contained large numbers of ephemeropteran
nymphs and megalopteran larvae. Odonate naiads, including both damsel- and
dragonflies, were taken by juvenile largemouth bass, warmouth, and green
sunfish. Included were species of clambering damselfies typically found in beds
of aquatic plants (see also Weaver and Zeibell 1976). Chironomids also were
taken by the last three fishes. Bluegill depended strongly on chironomids, along
with zooplankton (Table 1 ). Redear sunfish ate chironomid larvae only infre-
quently.
Mouthbrooder and striped mullet contained a few tiny chironomid larvae that
may have been consumed along with detritus (especially in the latter). Mouthb-
rooder, however, contained a' few terrestrial insects and a number of other
benthic groups.
Introduced palaemoneid shrimp, Palaemonetes paludosus, are common in the
lower Colorado River, but contributed to the diet of only five fish species. Black
crappie appeared to select the food item. Largemouth bass, warmouth, and
green sunfish all fed on shrimp at about the same proportion. Channel catfish
contained them at a frequency of only 3.7%. Perhaps its semi-transparent body
makes the shrimp relatively immune to all except special predators, especially
when in dense aquatic vegetation.
The introduced crayfish, Procambarus clacki, was a major food of almost all
large carnivores, especially catfish and smallmouth bass. Rainbow trout, carp,
largemouth bass, warmouth, green sunfish, and black crappie also ate the deca-
pod. Edwards (1974) reported crayfish from striped bass stomachs. Introduced
softshelled turtle, Trionyx spiniferus, also depended heavily on them (present in
10 animals dissected, along with odonate naiads as the only other food itern).
Asiatic clams were eaten by carp, channel catfish, yellow bullhead, redear
sunfish, largemouth bass, and mouthbrooder (Table 1). In all but redear sunfish,
clams were digested without breakage of valves, with the shell simply passing
through the intestinal tract. The redear sunfish is especially adapted for crushing
mollusks, with molariform teeth on its pharyngeal bones; however, less than
20% of shells in redear stomachs had been physically damaged. Crushing of
clams is obviously not requisite to digestion since shells in hindguts of redear
sunfish and other species alike were devoid of flesh- Consumption of clams by
carp was spectacularly high in some instances, with some fish containing more
than 30. Some clams eaten by carp and channel catfish exceeded 2.5 cm across
the valves, but most were less than 1.0 cm.
Rainbow trout, two of the catfish, and all sunfishes excepting bluegill con-
tained other fishes. Channel and flathead catfishes, largemouth bass, warmouth,
and black crappie were the most piscivorous species. Edwards (1974) demon-
strated that striped bass in the Colorado River were also voracious piscine
predators (Table 1).
Threadfin shad was the exclusive fish eaten by trout. Largemouth bass also ate
shad, followed by red shiner, unidentified sunfish, unidentified fish, and other
largemouth bass. Channel catfish fed on shad and red shiner, unidentified cen-
trarchids, and other unidentified fish. Flathead catfish ate mostly red shiner and
mouthbrooder. Four flathead catfish each had eaten a single fish, each of a
different species (threadfin shad, carp, channel catfish, and undetermined cen-
trarchid). The warmouth was a specialized piscivore, feeding on poeciliids and
red shiner. Green sunfish were more opportunistic, eating small carp and uniden-